Hey there everyone! I made a new guide on how to make a Lootbox farm from Vault-Tec lunchboxes with the Fallout 4: Contraptions DLC.
Last guide I made on this topic was a Semi-Automatic farm, so I had to think of a way to make this work.
If you have any questions or tips, please do so!

I used a mod by the way, to make the hopper in the beginning and the end connect. But you can easily do this without mods. It's only necessary that the lunchboxes come back on the conveyor belt inside.

Steel goes into the Builder, where it collects 3 Steel to make the Vault-Tec Lunchbox. After that the lunchbox travels to the highest floor by several lifts.
Here you see the ending of all that transportation. When the lunchbox gets out of the lift, it goes through a laser, which gives a signal to a counter (on the right).
I placed 2 counters, so when the right counter goes past the count of 9, a signal is being given to the other counter. This way the left counter only gives a signal once every 100 boxes that travels through the laser.
In the picture it's on 98, so it's almost showtime!
Here I have an example of what happens when it hits 100.
The signal travels to a Pitcher, filled with frag grenades. The Pithcer gets turned on for a slight moment, making sure only 1 or 2 grenade(s) get out in the shute.
The explosion, as you can see, opens most of the lunchboxes and gives them a "nudge" into the big hopper.
Here you can see the shute from outside the building.
I have 2 conveyor belts, since I have 2 of those big hoppers. They collect the junk and lunchboxes and transport to a storage. But you can also filter the junk out and make sure the lunchboxes get back in the conveyor belt inside.

This is the loot:

• Plastic fork
  
• Plastic knife
  
• Plastic spoon
  
• Chalk
  
• Baseball
  
• Nuka-Cola
  
• Bubblegum
  
• Noodle cup
  
• Gum drops
  
• Dandy Boy Apples
  
• Pen
  
• Pencil

It is possible to get rarer loot, like Nuka-Cola Quantum. But as I said, it's rare.
I don't know if Luck plays a role, since you aren't really involved in this process. But please correct me if I'm wrong!